load extensions in builtin trap

ensures `get_ipython` et al. are available.
fix callbacks as optional in js kernel.execute

plus some doc fixes.
Mainly to fix some backward compatibility with examples here and there.
fix documentation and test of getoutput

it returns both stdout and stderr
closes gh-3280
allow test_process to succeed without python installed
Merge pull request #3301 from juliantaylor/no-python-test

allow python3 tests without python installed
Fix: "python ABS/PATH/TO/ipython.py" fails

The following line in setupbase.py was the problem.  It assumes
that your CWD is always at the repository root.  This patch removes
this assumption.

    execfile(pjoin('IPython','core','release.py'), globals())
Merge pull request #3276 from tkf/fix-setupbase

Remove assumption that setup is being run from repo root.
Typo : optionnal -> optional
Merge pull request #3294 from Carreau/jsfix

fix callbacks as optional in js kernel.execute
speed up AsyncResult._wait_for_outputs (don't waste 0.01 seconds)

Greatly reduces waiting time on ready() call for large calculations.
Merge pull request #3308 from akhmerov/master

Speed up AsyncResult._wait_for_outputs(0)

Greatly reduces waiting time on ready() call for large calculations.
further clarify Image docstring
Merge pull request #3285 from minrk/extension-builtins

load extensions in builtin trap
Merge pull request #3310 from minrk/imagedocstring

further clarify Image docstring